posted by leann .
what is the formula for gravitational potential energy?
That depends upon whether you are talking about near the surface of the earth or farther away, where the gravitational force diminishes with the inverse square of the distance.
Near the Earth's surface, the gravitational potential energy is
P.E. = M g H,
where H is the height above some reference plane (such as sea level). M is the mass and g is the acceleration of gravity.